Effects of multiple-dose intranasal oxytocin administration on social responsiveness in children with autism: a randomized, placebo-controlled trial

Background Intranasal administration of oxytocin is increasingly explored as a new approach to facilitate social development and reduce disability associated with a diagnosis of autism spectrum disorder (ASD). The efficacy of multiple-dose oxytocin administration in children with ASD is, however, not well established. Methods A double-blind, randomized, placebo-controlled trial with parallel design explored the effects of a 4-week intranasal oxytocin administration (12 IU, twice daily) on parent-rated social responsiveness (Social Responsiveness Scale: SRS-2) in pre-pubertal school-aged children (aged 8–12 years, 61 boys, 16 girls). Secondary outcomes included a questionnaire-based assessment of repetitive behaviors, anxiety, and attachment. Effects of oxytocin were assessed immediately after the administration period and at a follow-up, 4 weeks after the last administration. The double-blind phase was followed by a 4-week single-blind phase during which all participants received intranasal oxytocin. Results In the double-blind phase, both the oxytocin and placebo group displayed significant pre-to-post-improvements in social responsiveness and secondary questionnaires, but improvements were not specific to the intranasal oxytocin. Notably, in the single-blind phase, participants who were first allocated to intranasal placebo and later changed to intranasal oxytocin displayed a significant improvement in social responsiveness, over and above the placebo-induced improvements noted in the first phase. Participants receiving oxytocin in the first phase also showed a significant further improvement upon receiving a second course of oxytocin, but only at the 4-week follow-up. Further, exploratory moderator analyses indicated that children who received psychosocial trainings (3 or more sessions per month) along with oxytocin administration displayed a more pronounced improvement in social responsiveness. Limitations Future studies using larger cohorts and more explicitly controlled concurrent psychosocial trainings are warranted to further explore the preliminary moderator effects, also including understudied populations within the autism spectrum, such as children with co-occurring intellectual disabilities. Conclusions Four weeks of oxytocin administration did not induce treatment-specific improvements in social responsiveness in school-aged children with ASD. Future studies are warranted to further explore the clinical efficacy of oxytocin administration paired with targeted psychosocial trainings that stimulate socio-communicative behaviors. Trial registration The trial was registered with the European Clinical Trial Registry (EudraCT 2018-000769-35) on June 7th, 2018 (https://www.clinicaltrialsregister.eu/ctr-search/trial/2018-000769-35/BE). Supplementary Information The online version contains supplementary material available at 10.1186/s13229-023-00546-5.

Further, children who already received OT in the double-blind phase, were also given another four-week course of OT administration during the subsequent single-blind phase. A cross-over of this group to the placebo nasal spray was deemed suboptimal, considering recent notions of long-lasting retention effects upon multiple-dose oxytocin administration [1], which may have interfered with a true assessment of placebo nasal spray administration. Furthermore, allowing the oxytocin-first group to receive an additional four-week course of OT allowed an exploratory examination of potential augmenting effects upon receiving the nasal spray for a longer duration.
COVID-19 related impact. As indicated in the initial EudraCT trial registration, participants were recruited to participate in a larger project, also including physiological, neural, neurophysiological and biological assessments, for which a total sample size of 60 participants was planned (30 in each treatment arm). However, due to COVID-19 related health restrictions, all physiological, neural and neurophysiological data collections were temporarily halted, resulting in extensive loss of treatment follow-up data on these neural outcomes. Fortunately, for all participants already enrolled or scheduled to initiate the nasal spray administration, the collection of the behavioral data through questionnaires could still be continued during the COVID-19 lock-down periods. Nonetheless, to account for the extensive data loss on the neurophysiological assessments, and upon approval from the Ethical committee, recruitment was extended after the COVID-19 lock-downs, allowing to still obtain the initially planned sample size of 30 participants in each treatment arm on the neurophysiological assessments.
As a result, the total sample size of participants in the trial (and for whom behavioral collections were performed) was increased from 60 to 80.
Reference: [1] Bernaerts S, Boets B, Bosmans G, Steyaert J, Alaerts K. Behavioral effects of multipledose oxytocin treatment in autism: A randomized, placebo-controlled trial with long-term follow-up. Mol Autism. 2020;11:6. Supplementary Table 2 Detailed information on medication use and co-occurring conditions for participants of the oxytocin and placebo treatment groups.

Supplementary
Current psychoactive medication use was defined as use within four weeks before study enrollment.
Co-occurring conditions were screened through parent-report (with the explicit mentioning of examples in the screening interview including e.g., ADHD, depression, dyscalculia, dyslexia).
All participants had a stable background treatment for at least four weeks prior to the treatment allocation and changes in medication regime were screened and logged. Supplementary Table 3 Side effect screening.

Oxytocin
Participants (with the help of their parents) were asked to administer the nasal spray (oxytocin or placebo) daily for four consecutive weeks in phase I (double-blind phase) and another four weeks in phase II (single-blind extension phase). At the end of each week, parents were asked to report whether their child presented any of the listed (or other) side effects and to indicate the severity of the side effect (mild, moderate, or severe). Safety analyses included all participants that received the allocated intervention. Panel C lists any other incidental adverse event, spontaneously reported by the parents.
While on average, no group differences were evident in the total proportion of reported side effects, a group differences was observed in the proportion of participants who reported moderate side effects in the last week of administration, indicating that the participants of the oxytocin group reported a slightly higher number of moderate side effects during that week.
When examined separately for each side effect, a higher proportion of participants of the oxytocin group reported to experience a 'headache' or 'abdominal/stomach pain' during the third week of the phase I treatment. Also a higher proportion of participants of the placebo group were noted to experience a 'sore throat' and to feel 'more confident', compared to the oxytocin group, but only during the first week of the phase I treatment.
In the single-blind phase (phase II), no significant group differences were revealed, either in the total proportion of reported side effects (Panel A) or separately for each side effect (Panel B).   Table 4 Daily screenings of changes in affect and arousal.
Both participants and their parents completed a structured daily diary for four consecutive weeks in phase I (double-blind phase) and another four weeks in phase II (single-blind extension phase). Once daily, parents were asked to complete two 9-point Manikin rating scales, rating their child's perceived arousal (1= calm, 9= excited) and valence (1= feeling pleasant/happy, 9= feeling unpleasant/unhappy; [1]). Children also completed a self-report of the arousal and valence scale, twice-daily, once at noon and once in the evening.
To examine treatment-related differences in the daily screenings, weekly averages were calculated for each rating and subjected to a general linear model with the within-subject factor 'week' (week 1-4) and the between-subject factors 'treatment' (oxytocin, placebo).
None of the scales yielded a significant main effect of 'treatment' across weeks (all, p > .05), indicating no overall significant group differences in ratings of valence or arousal, either by the parents or by the child, both in phase I and phase II.
Closer analysis of treatment effects separately for each week revealed a significant group difference in child-ratings of valence (in the evening), indicating higher feelings of 'unpleasantness' in the oxytocin, compared to the placebo group during the second week of the phase I treatment. Also in the first week of phase II, a similar effect was noted, indicating that children who crossed over from the placebo treatment (in phase I) to the oxytocin treatment (in phase II) (placebo-first group) reported slightly higher feelings of 'unpleasantness', compared to children who were receiving their second course of oxytocin treatment (oxytocin-first group).
In the table below, weekly averages (and average responses across the four weeks) are reported separately for each treatment group (oxytocin, placebo) and phase (phase I and II). P-values correspond to independent-sample t-tests (or F-tests) assessing between-group differences in ratings of arousal and valence. Data printed in bold show p-values equal to or larger than 0.05.
Notably, for several of the scales, the general linear model also revealed a main effect of 'week', indicating that across treatment groups, both parents and children reported improvements in reports of valence (more pleasant) and arousal (more calm) from the first to the last week of the trial, particularly in phase II, when all children received the 'actual' oxytocin treatment (phase II, parent-reported valence:  Supplementary Table 7 Effects of oxytocin nasal spray administration on primary and secondary outcome measures of the single-blind phase II. Changes from assessment session T2 (last session of phase I) are listed separately for the post assessment session (immediately after the four-week oxytocin nasal spray administration period, T3) and the follow-up assessment (four weeks after cessation of the nasal spray administration period, T4).